The present invention relates to a golf club, and more particularly to a golf club having novel means connecting the head and the shaft together.
There are two conventional means of forming a golf club by joining the club shaft, with its grip end and an opposed hollow end, to a club head, including a body and a hosel. In one alternative, the head defines a female hosel into which the male end of the shaft (whether hollow or solid) is inserted, with the male and female elements being secured by a glue or bond line between the outside diameter of the shaft and the inside diameter of the female hosel. Alternatively, the head defines a male hosel over which the hollow female end of the shaft is inserted, with the male and female elements being secured together by a glue or bond line between the inside diameter of the shaft and the outside diameter of the hosel. In both instances, however, a glue or bond line of at least 11/4 in. is required in order to provide the minimum surface area contact between the shaft and the head necessary to achieve the desired level of bonding therebetween. In particular instances, in addition to the bond line provided by the adhesive (typically epoxy), the bonding of the shaft and head is in some cases increased by press fitting of the shaft and hosel together, and/or even by the use of rivet pins extending through the hosel and shaft. In addition to the obvious necessity of securing the head to the shaft in order to form the golf club, the secure attachment between the shaft and head is necessary to provide an effective transmission of impact.
The ability of the shaft to flex adjacent the head is very beneficial to both the feel and performance of the club. While the shaft of the golf club (especially if hollow) is capable of a limited amount of flexing so as to impart a desirable whipping action to the golf ball upon impact, the design and construction of the hosel typically does not admit of such flexing of the hosel. Accordingly, where the shaft end and hosel overlap, the shaft within the female hosel or about the male hosel is precluded from the desired flexing. The greater the overlap of the hosel and shaft end, the greater the restriction on flexing of the shaft adjacent the head, and thus the poorer the performance of the club. Accordingly, the length of the overlap is a compromise between the desire to increase the bond line length (along the axis of the shaft) to provide a secure attachment of the shaft and head together, and the desire to decrease the bond line length in order to minimize the degradation of the performance of the club. According to either of the conventional constructions described above (that is, either the female hosel or the male hosel), approximately the same minimum bond line length of about 1.25 inches is required so that there is necessarily about the same minimum level overlap and hence the same deterioration of club performance.
Conventionally golf club shafts are made of either steel or graphite. The graphite shafts are normally lighter (i.e., less dense) than steel shafts Accordingly, a graphite shaft requires a golf club head that is heavier than that required for a steel shaft in order to maintain the same swing weight for the two clubs. Swing weight is a moment factor that is increased or decreased by increasing or decreasing the static weight of the head. Thus, it is impossible to use the same head with both steel and graphite shafts without affecting the swing weight of the complete golf club. Additionally, particular golfers will prefer slightly higher or lower swing weights for their clubs. Thus, it would be highly desirable to enable the swing weight of the club to be varied easily in order to meets the desires of particular golfers or the particular shaft with which a head is to be used, without a need for changing the head or or using a special head.
The normal manufacturing process for a golf club head rarely yields production volumes having a uniformity better than +/- 3 grams. A +/- 3 gram range yields finished clubs that are inside a range of approximately 4 swing weight units. An ideal assembled tolerance would be +/- 0.5 swing weight units. In order to compensate for these variations in the normal manufacturing process or to personalize the club for a particular user, the head weight is conventionally varied by using more or less adhesive or glue at the hosel/shaft overlap to increase or diminish the weight of the head and thereby bring the club into the desired swing weight range. This method of adjustment is not recommended, however, as too great a reduction in the amount of the adhesive used to connect the hosel and the shaft may diminish the security with which the head and shaft are secured together. In any case, the amount of adjustment possible by this method is limited by the typically low density of the adhesive. Another method of adjusting the swing weight of the club is to insert high density lead slugs within the shaft hollow end when the clubs are too light. These slugs must be soldered or otherwise securely attached to the shaft in order to preclude them from separating from the shaft during use of the golf club, thereby increasing the cost of materials and labor.
Accordingly, it is an object of the present invention to provide a golf club construction in which a bond line of reduced length provides an attachment of equivalent security between the shaft and the head.
Another object is to provide such a golf club construction which enables a minimum overlap of the shaft and head so as to improve golf club performance without impairing the security of the attachment of the head and the shaft.
A further object is to provide such a golf club construction in which the swing weight can be varied without changing the club head in order to accommodate different shaft types.
It is also an object of the present invention to provide such a golf club construction which facilitates adaptation of the golf club swing weight to the taste of a particular user.
It is a further object to provide such a golf club construction which facilitates compensations for manufacturing variations in head weight.